Illumination systems are used in many different applications, including projection display systems, backlights for liquid crystal displays and the like. Often, projection systems use one or more white light sources, such as high pressure mercury lamps. However, increasingly, light emitting diodes (LEDs) have been considered as alternatives to other white light sources. LEDs have the potential to provide the brightness and operational lifetime that would compete with conventional light sources. Current LEDs, however, especially green emitting LEDs, are relatively inefficient.
Because of this inefficiency, wavelength converted light emitting diodes (LEDs) are becoming increasingly important for illumination applications where there is a need for light of a color that is not normally generated by an LED, or where a single LED may be used in the production of light having a spectrum normally produced by a number of different LEDs together.
One approach to generating white light with a single LED is to first generate blue light with the LED and then to convert some or all of the light to a different color. For example, a portion of the blue light may be converted to red light, and a portion of the blue light may be converted to green light, such that the resultant output light, when mixed, is white. One common problem, however, when utilizing such a system of light converting layers is that a good deal of light may be reabsorbed by the light converting layers after an initial color conversion. In particular, green light that is converted from blue light is at risk for being absorbed by red potential wells. Such absorption can have negative effects on both the desired color balance of the light emitting system, as well as its efficiency. It would be desirable to provide a light converting LED that was capable of minimizing green light absorption.